Flange, also known as a flange disk or boss, is a component used for connecting shafts or for joining pipe ends; it's also used at equipment inlets and outlets, such as reducer flanges. A flange connection or flange joint refers to a removable connection made up of the flange, gasket, and bolt, acting as a combined sealing structure. Pipe flanges are the flanges used for piping in pipeline installations, or for equipment inlets and outlets on equipment. Flanges have holes, and bolts are used to tightly secure the two flanges together. They are sealed with a gasket. Flanges come in threaded (screwed) connections,焊接 (welded) flanges, and clamp flanges. Flanges are always used in pairs; low-pressure pipelines can use threaded flanges, while those over four kilograms of pressure use焊接 flanges. Two flange disks are joined with a sealing gasket and then tightened with bolts. Flanges of different pressure ratings have different thicknesses and require different bolts. When pumps and valves are connected to pipelines, the respective parts of these equipment are also made in the shape of corresponding flanges, also known as flange connections. Any connection component that uses bolts to connect two flat surfaces around the edges and seal them is generally called a "flange," such as in the case of ventilation pipe connections. These types of components can be referred to as "flange-type parts." However, such connections are only part of a single piece of equipment, like the connection between a flange and a pump, so it's not appropriate to call the pump a "flange-type part." Smaller items like valves can be called "flange-type parts."